In many applications, it is desirable to take two or more, highly comparable photographs of an organic or otherwise changing or moving subject at two separate times. This can involve acquiring the photographs in a manner that ensures the subject is in substantially the same position in both photographs and that the relative position and orientation of the camera to the subject is substantially the same in both photographs. For example, suppose a plastic surgeon is performing neck lift surgery on the neck folds of a patient and desires, accordingly, to acquire a series of images of the patient before, during, and after surgery to record changes in skin color, elasticity (e.g., how the skin hangs), etc. From one image to another, these changes can be difficult to reliably compare optically if there is any appreciable change in the position or orientation of the camera, in the position or orientation of the patient's head, in the shape and/or size of the target region (e.g., if there is a reduction in swelling), etc. Accordingly, many traditional image registration approaches (e.g., mapping of features from one image to another) can be ineffective or sub-optimal.
While there are a number of conventional approaches to maintaining the positions and/or orientations (relative and/or absolute) of the subject and/or the acquisition device (e.g., the camera), most involve a physical structure that guides and/or holds the subject and/or the camera. For example, one system includes a bar that extends from a camera by a set distance, which, by holding the end of the bar against the subject, can ensure the camera is positioned a fairly consistent distance from the subject in multiple sessions. However, this approach does little to ensure that the camera is in the same overall position and orientation with respect to the subject from one acquisition session to another, and it does essentially nothing to ensure that the subject is in the same position from one acquisition session to another. Some other systems include boxes, platforms, and/or other structures to guide or even hold a subject in a particular position relative to a fixed camera. These approaches can hold both the camera and subject in a relatively stable relationship, but they generally involve specialized structures, which are often large, heavy, expensive, and difficult to configure.